1. Field of Invention
The invention relates to a method and device for the installation of on-site sewage treatment and disposal systems and in particular to drainfield installation and drainfield pipe.
2. Background Art
As defined in the Florida Administrative Code, Rule 10D-6, Department of Health and Rehabilitative Services, Standards for Onsite Sewage Treatment and Disposal Systems, onsite sewage treatment and disposal systems comprise a sewage treatment and disposal facility, that contains a standard subsurface, filled or mound drainfield system, an aerobic treatment unit, a grey water system tank, a laundry wastewater system tank, a septic tank, a grease interceptor, a dosing tank, a solids or effluent pump, waterless, incinerating or organic waste composting toilets, or a sanitary pit privy that is installed beyond a building sewer on land of the owner or on other land to which the owner has the legal right to install a system. As further defined in the above referenced Code, a drainfield comprises a system of open jointed or perforated piping, approved alternative distribution units, or other treatment facilities designed to distribute effluent for filtration, oxidation and absorption by the soil within the zone of aeration. Further defined in the Code, is a septic tank, which is a watertight receptacle constructed to promote separation of solid and liquid components of wastewater, to provide limited digestion of organic matter, to store solids, and to allow clarified liquid to discharge for further treatment and disposal into the drainfield.
Typically, drainfields are "standard subsurface systems", "filled systems", or "mound systems." The above referenced Code defines a standard subsurface drainfield system as an onsite sewage treatment and disposal system drainfield consisting of a distribution box or header pipe and a drain trench or absorption bed with all portions of the drainfield sidewalls installed below the elevation of undisturbed native soil. A filled system is defined as a drainfield system where a portion, but not all, of the drainfield sidewalls are located at an elevation above the elevation of undisturbed native soil on the site. Mound systems are defined as drainfields constructed at a prescribed elevation in a prepared area of fill material. All drainfields where any part of the bottom surface of the drainfield is located at or above the elevation of undisturbed native soil in the drainfield area is a mound system.
Drain trenches and absorption beds are the standard for drainfield systems used for disposing of effluent from septic tanks or other sewage waste receptacles. An absorption bed comprises an area in which the entire earth content to a specified depth in the required absorption area is removed, replaced with aggregate to that specified depth, and distribution pipe or other approved drainfield components. The distance between the centers of the distribution lines in standard beds is to be a maximum of 36 inches in order to meet the above referenced Code. Further, the distance between the side wall of the bed and the center of the outside drain is to be no more than 18 inches, but shall not be less than six inches. Header pipe is to extend to within 18 inches of the side walls. The maximum depth from the bottom of the drainfield to the finished ground surface shall not exceed 30 inches after natural settling. The minimum earth cover over the top of the drainfield, distribution box or header pipe in standard subsurface drainfields shall be 6 inches after natural settling. By way of example, depending on the type of drainfield system being utilized, the drainfield absorption surface is to be constructed level or with a downward slope not exceeding one inch per 10 feet. Such requirements, although given here for one state, are typical of the stringent requirements for drainfields. When one considers the lightweight, flexible polyethylene pipe typically used in such drainfields, and the aggregate of heavy gravel, it is appreciated that holding to such dimensional code requirements is difficult, time consuming and costly. A typical system might include a four inch minimum inside diameter having two rows of holes having a specified perforated area. The perforations must be located at a particular angle from a vertical on either side of centerline of the bottom of the pipe. Further, the pipe must be installed so that the perforations are effective in the effluent treatment. Twisting of the pipe can cause a hole to be at the very bottom during installation. Such a condition will not meet Code and will not pass an inspection. It is required that the perforations be such that the effluent is distributed as equally as possible throughout the drainfield area. It is not unusual for a standard drainfield installation to take a three man crew with back hoe more that a day to install a typical standard subsurface drainfield to within Code tolerances. It is also well known that many installations have to be reinstalled because an inspector failed the original installation because a grade or separation dimension was not met.
As described in U.S. Pat. No. 5,015,123 to Houck et al., conventional drainage systems of the type described and to which the present invention relates typically comprise horizontally extending corrugated and perforated plastic pipe placed within the drainfield area surrounded by a quantity of loose aggregate material, such as rock or crushed stone. By way of example and in the case of the standard subsurface drainfield, the space between the conduit and the ground occupied by the aggregate defines a drainage cavity in fluid communication with the perforations of the conduit. Such a nitrification field comprises effluent discharging from a septic tank through the perforated pipe of a nitrification line which in surrounded by a specified minimum volume of aggregate material, such as rock or crushed stone. The nitrification field creates a storage area for sewage effluent to be absorbed by the soil. The aggregate maintains the boundaries of the storage area, prevents blockage of the pipe perforations, and promotes the beneficial effects wherein aerobic bacteria organisms act on the sewage colloidal materials to reduce them in the soil. The perforated conduit serves the purpose of delivering the effluent to the aggregate filled cavity for absorption into the soil and to vent sewage gases for preventing local contamination. The use of corrugated pipe permits the trapping of effluent for a secondary, a semi-aerobic treatment within the pipe corrugations.
Houck '123 particularly discloses a method and apparatus for the installation of a drainage field. Houck '123 describes a method and apparatus that employs a preassembled drainage line unit for placement in a trench which provides a uniformity and ease of installation. The preassembled drain line comprises loose aggregate in the form of light weight materials in a surrounding relationship to perforated conduit bounded by a sleeve member. As stated by Houck '123, the requirements for uniformity and inspections for compliance with state and local codes makes the drainfield installation process tedious and time consuming. Houck '123 looks away from the teachings of the standards employing typical gravel aggregate to fill a trench or absorption bed.
U.S. Pat. No. 4,268,189 to Good discloses an apparatus and method for supporting and positioning pipe during the construction of drain fields and the like. The apparatus comprises a horizontal elongate support member with spaced apart clamping units thereon arranged for suspending flexible pipe sections from the elongate support member. The elongate support member is adjustably supported for vertical adjustment on substantially vertically disposed elongate anchoring members adapted to be driven into a grade surface so as to firmly anchor the respective pipe supporting apparatus against displacement in order to maintain the same and the pipe sections supported thereby against horizontal or vertical displacement during the pouring and spreading of aggregate around the pipe sections. The arrangement facilitates the subsequent releasing of the pipe sections from the pipe supporting apparatus and the removal of the pipe supporting apparatus from the aggregate while leaving the corresponding pipe sections embedded in the aggregate. As addressed in the Good '189 patent, the proper positioning of flexible pipe during the construction process has met with difficulty, since such pipe must be maintained in a proper position while being surrounded by the aggregate, as herein earlier described. Clamping the flexible pipe from the sides and below, although securing the pipe during aggregate pouring, can cause movement in the pipe when the apparatus is being pulled from the aggregate. Further, the combination of the elongate horizontal support member and fixed clamping members limit flexibility of use in varying length pipe runs and varying absorption bed layouts. Convenience and ease of use is desirable during the construction process.
U.S. Pat. No. 5,242,247 to Murphy discloses a pipe laying apparatus for maintaining the pipe placement during substantial completion of back filling of a trench in which the pipe is being laid. The apparatus comprises a shaft having an adjustable sleeve and an adjustable pipe grasping sleeve adapted for engagement to a variety of sized pipes. The apparatus is securely placed in to the trench by manual manipulation of handles or by striking a strike plate with a hammer. Murphy '247 addresses the need for fast and convenient removal of the apparatus from a trench. The use of multiple pipe-holders provides such convenience. However, the apparatus as disclosed by Murphy '247 comprises a pipe support placed below the pipe for holding the pipe at a fixed level. In operation, after backfilling a trench to a level above the pipe, the apparatus is rotated ninety degrees for lifting out of the trench while the pipe remains in place. With drainfields using flexible corrugated and perforated flexible pipe surrounded by aggregate material typically of stone, gravel and the like, rotating the apparatus becomes difficult and causes the flexible pipe to be displaced proximate the apparatus.
U.S. Pat. No. 3,568,455 to McLaughlin et al. discloses a method of laying pipe in a bed of particle material. A series of posts are removably mounted at spaced positions on the ground along the course of the pipe. The pipe is releasably supported on the posts in a raised condition above the ground while particle material is deposited under the pipe to at least a depth at which the deposit can sustain the pipe in its raised condition. The pipe is released from the support of the posts, and the posts are removed from the deposit while the deposit sustains the condition of the pipe. McLaughlin '455 discloses a bracket plate having an arcuate indentation for mating with the top cylindrical surface portion of various sized pipe. The pipe is held in communication with the arcuate indentation by a flexible cable which wraps around the bottom portion of the pipe while being hingedly attached to one end of the plate and removably connected to an opposing end for securing the pipe in place. Once the trench has been backfilled, the cable is released from the plate opposing end and the device is lifted from the backfilled trench. Although very effective for generally light materials and generally rigid pipe, again, difficulty occurs when using the flexible corrugated pipe and aggregate combination as earlier addressed. The cable wrapped around the pipe dislodges the pipe from its position as the device is pulled from its position.